The focus of the research in the laboratory ‘Forschungskraftwerk’ is the development and demonstration of innovative, fuel-flexible, low emission and highly efficient decentralized power plant concepts. The CHP test rigs in the lower output range of up to 30 kWel are used as a basis for investigating the properties and operating performance of micro gas turbines experimentally and studying new wiring and coupling concepts.
The laboratory is designed for power plants with an air mass flow of up to a 4500 Nm³/h of filtered ambient air and a maximum feed of 100 kW of electrical output. The laboratory is also equipped with compressed air at 10 and 12 bar. Besides a supply of natural gas (up to 18 bar) and a supply of liquid fuel via a liquid fuel tank, additional fuel can be supplied via an external gas storage. The required gas mixtures can be composed from the separate gases H2, O2, CH4, CO, CO2 and N2 with the synthesis gas facility. A comprehensive safety concept that monitors gas leakage and has an automatic switch-off guarantees safety in the laboratory.
The process control system for monitoring and controlling the test rigs and systems is managed from a separate control room. Depending on the requirements, all relevant parameters such as mass flows, temperatures, pressures and acoustic fluctuations can be recorded for all the test rigs using a measurement data acquisition system.
Another part of the basic equipment for the measurement technology is an exhaust gas analysis, which can be used to continuously measure the O2, CO, CO2, NO, NO2, UHC and H2O content of the exhaust gas.
An OH* chemiluminescence camera is available to capture the flame shape, distribution and position. Furthermore, laser-based methods from the Department of Laser Diagnostics are used for detailed examination of the flow and combustion processes.
In Forschungskraftwerk, there are currently two test units based on the EnerTwin type micro gas turbine manufactured by Micro Turbine Technologies BV, and there will soon be a Garrett GTCP 36-28 type test unit available for research purposes.
The micro gas turbines are used for ongoing development of the combustion systems and as a basis for innovative micro gas turbine-based CHP / APU concepts. Key research activities are the reduction of pollutant emissions, the reliability of technical combustion systems and the use of flexible fuels.
The micro gas turbines are equipped with in-depth measurement technology to enable investigation of the individual system components as well as the entire system.
The data acquired in the experiments is used to validate system cycle and combustion simulation models.
At present, the micro gas turbines are being used to study a FLOX® combustion chamber developed in our Institute under realistic operating conditions, and to investigate the inverted Brayton cycle (-> IBC) and a hybrid power plant consisting of a micro gas turbine and a fuel cell (-> HyKW). In addition to the EnerTwin micro gas turbine, a test unit based on a GTCP 36-28 auxiliary power unit (APU) is currently under construction (-> APU).
Overview of the EnerTwin micro gas turbine unit
The EnerTwin micro gas turbine delivers 3 kW of electrical power and 14 kW of thermal power. The micro gas turbine compresses ambient air to 3 bar (full load) via a radial compressor. Before feeding the air into the combustion chamber, it is pre-heated to around 700 degrees Celsius in a recuperator. The recuperator is used to increase the level of electrical efficiency by using the waste heat of the exhaust gas downstream of the turbine to pre-heat the air. The pre-heated air reacts with the injected fuel in the combustion chamber. The hot exhaust gas produced is expanded in the turbine to ambient pressure. The exhaust gas, which can be up to 800 degrees Celsius, is then fed to the recuperator, which transfers some of the residual heat to the inlet air. A downstream water heat exchanger used for generating central heating is used to cool the exhaust gas to a temperature of 20-50 degrees Celsius depending on the connected heating system.
The turbine, compressor and electrical generator are located on one shaft that rotates at a maximum rotation rate of 240,000 rpm. The high-frequency alternating current generated by this is first converted into direct current by the power electronics and then into the desired network frequency and network voltage.
Overview of the GTCP 36-28 auxiliary power unit
The GTCP36-28 micro gas turbine is an auxiliary power unit (APU) for a VFW 614 aircraft, supplying it with electrical power and compressed air for engine start-up and air conditioning. In the Forschungskraftwerk, the connection to the on-board power and compressed air circuits on the aircraft is simulated by appropriate control elements. The APU is operated at a fixed rotation rate of 59,200 rpm and generates 23 kW of electric power. All of the process and compressed air is boosted by a single stage centrifugal compressor – the compressed air is extracted immediately downstream of the compressor and fed into the aircraft's on-board electrical system. It has a minimum total pressure of 3 bar. In addition, the process air flows into the combustion chamber downstream of the compressor, where it reacts with the injected kerosene. The hot exhaust gases are then expanded by the radial turbine and exit the system at an exhaust gas temperature of 620 degrees Celsius. In the original design, the unit is operated without a recuperator. In the laboratory Forschungskraftwerk, the GTCP 36-28 is used as a new testing platform for new APU circuits and components.